One fundamental method to investigate biological processes is by loss-of-function studies. The goal of these efforts is to determine the activity of a gene by disrupting that gene and monitoring the effects on a biological system. Recently, gene targeting technology has been developed using zinc finger nucleases (ZFNs) as a method to mutate specific genes. The approach involves engineering zinc finger DNA binding domains to recognize specific target sequences. These domains can then be tethered to the FOK1 exonuclease domains to generate a fusion protein that can induce double stranded DNA breaks near the zinc finger binding sites. ZFNs have been successfully used to disrupted genes in a variety of systems ranging from plants to mammals. Thus far, only a relatively small number of laboratories have reported successful efforts to employ ZFNs. The use of ZFNs has been curtailed by the difficulty in generating zinc finger domains that bind to specific target sequences, and by the high cost of commercially available ZFNs. In preliminary studies, computer aided modular design has been an effective means to engineer functional ZFNs. The experiments in this application evaluate the effectiveness of a strategy to use modular ZFN design to generate germ-line mutations using zebrafish as a model system. Zebrafish is a powerful system for genetic, cellular, and molecular studies, and the ability to routinely perform gene targeting studies would be a major advance. The methods in this application are broadly applicable to biomedical research in both cell culture systems and model organisms. RELEVANCE: The human genome project has identified thousands of novel genes, but the activity of many of these genes remains unknown. The ability to disrupt specific genes is a powerful means to determine the function of these genes. The experiments in this application evaluate the effectiveness of one means to accomplish this goal using model organisms and cell culture systems.